Computers use social media data to predict crime

Algorithms can now predict the time and place of various crimes by analysing location-based data from social media users.

In a study published in the EPJ Data Science journal, RMIT researchers used location and activity data from Foursquare app users in New York City and Brisbane to predict specific types of crime.

Foursquare users share their location and activity when they 'check-in' at various places. The study used data from over 20,000 check-ins by users in Brisbane, and nearly 230,000 check-ins by users in New York City.

RMIT computer scientist Dr Flora Salim says this dynamic, real-time data on people movements around a city is highly valuable in understanding the likelihood of different situations in an area.

But to fill the many gaps in this location-based data, researchers also developed recommendation algorithms, similar to those used to recommend related songs on Spotify.

“Obviously the large majority of people in the city were not always using the app and those committing crimes were likely not posting on the app about it,” she says. “So, we used recommender systems to fill in the gaps and predict other activities in any given scenario.”

In tests on both cities, the system predicted specific types of crime in specific parts of the city better than existing crime prediction models based on crime trends.

In Brisbane, the system was found to be 16 per cent more accurate at predicting assaults than current models, 6 per cent more accurate for predicting unlawful entry, 4 per cent better for drug offences and theft and 2 per cent better for fraud prediction.

In New York City, it improved prediction accuracy by 4 per cent for theft and drug offences, fraud and unlawful entry, while improving predictions of assault by 2 per cent.

Salim says that given the sparsity of data sets used in the study, these results are significant.

“Based on these positive results, this technology could allow police to design more effective patrol strategies with limited resources by sending officers to the places where crime is more likely,” she says.

The system is also able to be easily scaled up to process larger samples from almost any social media platform, app or mobile network that collects location-based data.

“The widespread use of social media such as Twitter and Foursquare - which all gather huge amounts of data on our location, activities and preferences - provides unprecedented opportunities to capture the movement and activity of people across a city,” she says.

The study is just one example of how our data can be used to predict our actions for a whole range of applications.

Another project Salim is involved in looks at algorithms to predict, with high levels of accuracy, what we’ll do in the second half of our day based on historic patterns and data collected from the first half of our day.

“Research into the pattern of human movement, based on data from our mobile apps, often shows how predictable many of our activities are,” Salim says.

Lead author and PhD student Shakila Khan Rumi, who is supervised by Salim and Dr Ke Deng, says the study marks a significant step forward on crime prediction models.